It seems that analysis of ancient rocks on both Earth and Mars has provided no evidence of greenhouse gasses as an explanation for warm wet environments under a faint young sun. When empirical evidence clashes with modelling it is prudent to re-evaluate the assumptions underpinning the model. One hypothesis that I find of interest is the possible effects of the solar system passing through interstellar dust clouds. There would be minimal attenuation of solar flux but the capture of molecular hydrogen would result in a significant increase in the sun's luminosity. McCrea, W.H. (1975). Ice Ages and the Galaxy, Nature 255, 607–609 suggests that an encounter with interstellar cloud densities of 10^5 to 10^7 H2/cm3 would increase the Sun’s luminosity by up to 100 percent during the course of an encounter.

Relatively small changes in conditions can lead to important changes in dynamics. An ancient Mars with slightly higher surface pressure would enable a liquid phase of matter.

However, it's not only different climates that allow this. Mars has higher subsurface pressure now than its surface pressure now. Water ice with a bit of regolith on top of it can reach conditions that allow a liquid phase. Boiling of that water would create rapid expansion that would move that regolith while relieving the pressure that enabled the liquid phase in the first place. Slightly different climates could allow profoundly different dynamics. There are a lot of variables to contend with.

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